What are microorganisms?

Some living things are just one cell, or a very few. They are far too small to see with the naked eye. These are microorganisms, or microbes: micro means very small, and organisms means living beings.

Some, like bacteria and Amoeba, are a single cell: unicellular. Others, like some fungi and algae, have many cells: multicellular. They are everywhere: in water, soil, air, and even inside your body.

Look for yourself (Activities 2.4 and 2.5). Put a drop of pond water or stagnant water on a slide under a coverslip and look through a microscope. Then stir some moist soil into water, let it settle, and look at a drop from the top. Both are full of tiny moving creatures.

What one Grade 8 class found (Activity 2.6):

So the main groups are protozoa, algae, fungi and bacteria. An easy way to remember them: B-F-P-A (bacteria, fungi, protozoa, algae).

A microscope magnifies them 100 to 400 times. Scientists have also made a cheap foldable paper microscope. It doesn't show the detail of a big laboratory microscope, but it lets many more people see the tiny world.

And there is a V to write separately: viruses. They are tiny too, but they are acellular: not made of cells at all. They multiply only once they get inside a living cell. They may infect plants, animals or even bacteria, and may cause disease.